Metalated porous porphyrin polymers as efficient heterogeneous catalysts for cycloaddition of epoxides with CO2 under ambient conditions

Article abstract of DOI:10.1016/j.jcat.2016.03.005

We have successfully synthesized a porphyrin based porous organic polymer (POP-TPP) from free-radical polymerization of tetrastyrylporphyrin monomer under solvothermal conditions. Besides high surface area (1200 m²/g) and high thermal stability, the obtained polymer features open metal chelating sites, and thus the catalytic activities of metalloporphyrins can be reasonably adjusted by introducing various metal ions. After metalation with Co³⁺, Zn²⁺, and Mg²⁺, the Co/POP-TPP, Zn/POP-TPP, and Mg/POP-TPP as heterogeneous catalysts are very active for cycloaddition of epoxides with CO₂ to cyclic carbonates at ambient conditions with n-Bu₄NBr as a nucleophilic additive. Particularly, under the relatively low CO₂ concentration (15% in volume), the activity of heterogeneous Co/POP-TPP catalyst is even higher than that of the corresponding homogeneous Co/TPP catalyst. More importantly, there is no activity loss even if the Co/POP-TPP is recycled for 18 times. The excellent catalytic activity and superior recyclability of the obtained catalysts indicate that the porphyrin based porous organic polymer is a promising candidate for construction of efficient heterogeneous catalysts in the future.

Full text of DOI:10.1016/j.jcat.2016.03.005

Journal of Catalysis 338 (2016) 202–209
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Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Metalated porous porphyrin polymers as efficient heterogeneous
catalysts for cycloaddition of epoxides with CO2 under ambient
conditions
Zhifeng Dai a, Qi Sun a, Xiaolong Liu b, Chaoqun Bian a, Qinming Wu a, Shuxiang Pan a, Liang Wang a,
Xiangju Meng a, , Feng Deng b, Feng-Shou Xiao a,
⇑
⇑
a Key Laboratory of Applied Chemistry of Zhejiang Province and Department of Chemistry, Zhejiang University, Hangzhou 310028, China
b State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China
a r t i c l e i n f o
a b s t r a c t
Article history:
We have successfully synthesized a porphyrin based porous organic polymer (POP-TPP) from free-radical
polymerization of tetrastyrylporphyrin monomer under solvothermal conditions. Besides high surface
area (1200 m2/g) and high thermal stability, the obtained polymer features open metal chelating sites,
and thus the catalytic activities of metalloporphyrins can be reasonably adjusted by introducing various
metal ions. After metalation with Co3+, Zn2+, and Mg2+, the Co/POP-TPP, Zn/POP-TPP, and Mg/POP-TPP as
heterogeneous catalysts are very active for cycloaddition of epoxides with CO2 to cyclic carbonates at
ambient conditions with n-Bu4NBr as a nucleophilic additive. Particularly, under the relatively low CO2
concentration (15% in volume), the activity of heterogeneous Co/POP-TPP catalyst is even higher than
that of the corresponding homogeneous Co/TPP catalyst. More importantly, there is no activity loss even
if the Co/POP-TPP is recycled for 18 times. The excellent catalytic activity and superior recyclability of the
obtained catalysts indicate that the porphyrin based porous organic polymer is a promising candidate for
construction of efficient heterogeneous catalysts in the future.
Received 15 October 2015
Revised 28 February 2016
Accepted 5 March 2016
Keywords:
Carbon dioxide
Porous organic polymer
Porphyrin
Cyclic carbonates
Heterogeneous catalysis
Ó 2016 Elsevier Inc. All rights reserved.
1. Introduction
Compared with the other catalysts, the metal-salen complexes
and metal-porphyrins can realize the transformation under rela-
Chemical fixation of CO2 to form economically valuable cyclic
carbonates has been paid much attention recently due to the com-
bination of the solution of CO2 greenhouse gas and the wide appli-
cations of the cyclic carbonates [1–4]. For this reaction, a number
of homogeneous catalysts such as ionic liquids [5,6], alkali metal
halides [7], metal salen complexes [8–13], and metalloporphyrins
[14–18], and heterogeneous catalysts such as metal oxides
[19–21], zeolites [22,23], ion-exchanged resins [24], mesoporous
materials [25–27], nanoporous polymers [28,29], and metal-
organic frameworks (MOFs) [30,31] have been employed. Notably,
most of these catalysts normally require harsh conditions such as
relatively high temperature, high CO2 pressure, and high catalyst
loadings. Undoubtedly, a catalyst system that is enabled to convert
CO2 at atmospheric pressure or even lower partial CO2 pressures
and room temperature with only heat from the surrounding
environment to avoid the generation of new CO2 is exceedingly
desirable [32,33].
tively mild conditions [34–40]. Particularly, when these active spe-
cies are immobilized in the porous materials [33,41–43] such as
zeolites [42], they exhibit not only high activities but also a long
catalyst life. In spite of this, these immobilized heterogeneous cat-
alysts generally show lower activities than the homogeneous coun-
terparts as a result of fewer accessible active sites in comparison
with the soluble ones [33,42,43]. Therefore, it is strongly desirable
to obtain the heterogeneous catalysts with both long catalyst life
and very high activities.
Recently, there are encouraging heterogeneous catalysts such as
Cu-MOF [44] and metal-salen based conjugated microporous poly-
mers (metal-salen-CMP) [45], exhibiting excellent catalytic perfor-
mance for production of cyclic carbonates, and even outperforming
the corresponding homogeneous catalysts under real mild condi-
tions such as at room temperature and atmospheric pressure
[44–46]. However, in these catalysts it is still observed a little
metal leaching.
More recently, it has been reported that porous organic
polymers (POPs) with excellent framework stabilities and hierar-
chical porosities are endowed with very high accessibility and
⇑
Corresponding authors.
E-mail addresses: mengxj@zju.edu.cn (X. Meng), fsxiao@zju.edu.cn (F.-S. Xiao).
http://dx.doi.org/10.1016/j.jcat.2016.03.005
0021-9517/Ó 2016 Elsevier Inc. All rights reserved.

Z. Dai et al. / Journal of Catalysis 338 (2016) 202–209
203
outstanding binding ability of catalytically active species [47,48].
For instance, Rh metalated porous organic ligand polymers of
triphenylphosphine (POL-PPh3) as heterogeneous catalysts exhibit
not only comparable activities and selectivities to those of the
homogeneous counterparts in olefin hydroformylations but also
extraordinary recyclabilities [49]. It is also shown that the meta-
lated (Fe and Mn) porous organic polymers (POPs) containing
free-base porphyrin subunits by the condensation of a bis(phthalic
acid)porphyrin with tetra(4-aminophenyl)methane [50] are very
active catalysts in both olefin epoxidation and alkane hydroxyla-
tion. Inspired by these successful examples, we have rationally
designed and synthesized a hierarchically porous organic polymer
(POP-TPP) constructed from polymerization of the vinyl-
functionalized tetraphenylporphyrin monomer (tetrastyrylpor-
phyrin). After metalation, these porous heterogeneous catalysts
with very high degree of the accessible active sites exhibit compa-
rable activities in cycloaddition of epoxides with CO2 to those of
the homogeneous catalysts. More importantly, there is no activity
loss even if the Co/POP-TPP is recycled for 18 times. Particularly,
when the concentration of CO2 is reduced to about 15% CO2 in
volume (the concentration of emission from the industrial pro-
cesses to the air), the Co/POP-TPP heterogeneous catalyst shows
even much better activity than the corresponding homogeneous
Co/TPP catalyst. The enrichment of the CO2 by the porous materials
is responsible for this phenomenon. Our work therefore provides
an avenue for energy-effective CO2 transformation in particular
for the direct conversion of industrial combustion CO2.
containing propionic acid (100 mL) preheated to 140 °C in air. After
reaction for 1 h, the solution was cooled to room temperature.
After filtering and washing with methanol and ethyl acetate as well
as drying, the title compound was obtained as purple crystals
(0.41 g, 22.6% yield). 1H NMR (CDCl3, 400 MHz): d 8.89 (s, 8H,
b-porphH), 8.17 (d, 8H, J = 8.0 Hz, PhH), 7.79 (d, 8H, J = 8.0 Hz,
PhH), 7.06 (m, 4H, CH@), 6.10 (d, 4H, J = 20.0 Hz, @CH2), 5.51 (d,
4H, J = 8.0 Hz, @CH2), and À2.75 (s, 2H, NH) ppm. 13C NMR (CDCl3,
100.5 MHz): d 141.69 (mesoporphC), 136.94 (ArC), 136.71 (C@),
134.84 (b-porphC), 124.62 (ArC), 119.91 (ArC), and 114.68 (@C)
ppm.
2.2.3. Synthesis of porous organic tetraphenylporphyrin polymer (POP-
TPP)
The POP-TPP was synthesized from a solvothermal polymeriza-
tion of the TSP monomer. As a typical run, 1 g of TSP was dissolved
in 10 mL of NMP, followed by the addition of 50 mg of AIBN. After
maintaining in an autoclave at 200 °C for 72 h, the POP-TPP pro-
duct with reddish brown color was finally obtained after washing
with DMF and purifying by Soxhlet extraction (CH2Cl2, 72 h;
0.96 g, 96% yield).
2.2.4. Synthesis of Co/POP-TPP
After degassing DMF (ca. 150 mL) with N2 for 5 min in a three
neck round-bottom flask, the POP-TPP (1 g) was added, and the
mixture was heated to 120 °C. Then, CoCl2Á6H2O (1.01 g) was
added, continuously stirring under N2 at 120 °C for overnight. After
cooling down to room temperature, HCl (3 M, 60 mL) was added
slowly into the mixture in the air. After filtering, washing with
water, drying in air, purifying by Soxhlet extraction, and drying
under vacuum condition, the Co/POP-TPP catalyst with brown
color was finally obtained (0.98 g, 90.3% yield).
2. Experimental
2.1. Materials
Tetrahydrofuran (THF) and N,N-dimethylformamide (DMF)
were distilled over LiAlH4 and CaH2, respectively. N-methyl-2-
pyrrolidone (NMP) was obtained from Aladdin (Shanghai), which
2.2.5. Synthesis of Zn/POP-TPP and Mg/POP-TPP
The synthesis of Zn/POP-TPP [52] and Mg/POP-TPP [53] was
very similar to that of the Co/POP-TPP, except for the use of differ-
ent inorganic cations and solvents. The Zn/POP-TPP and Mg/POP-
TPP were finally obtained as dark green and brown solids in
89.9% and 95.1% yield, respectively. The details are presented in
Supplementary Materials.
was
used
without
further
purification.
Pyrrole
and
4-bromostyrene were from Aladdin and Meryer Chemical Technol-
ogy (Shanghai), respectively, which were distilled before the use.
Other commercially available reagents [azobisisobutyronitrile
(AIBN), epichlorohydrin, propylene oxide, 1,2-epoxyhexane,
styrene oxide, allyl glycidyl ether, and butyl glycidyl ether] were
purchased with high purity and used without further purification.
2.3. Characterization
Nitrogen sorption isotherms collected at À196 °C were mea-
sured with Micromeritics ASAP 2020M systems, and the samples
were pre-treated under vacuum at 100 °C for 12 h. The surface
areas were calculated by the Brunauer–Emmett–Teller (BET)
method. CO2 sorption isotherms were collected from Micromeritics
ASAP2010 at 25 °C under the pressure of 1 atm CO2. Before the
measurement, the samples were treated under vacuum at 100 °C
for 12 h. X-ray Photoelectron Spectroscopy (XPS) spectra were per-
2.2. Catalyst preparation
2.2.1. Synthesis of 4-vinylbenzaldehyde
An excess of DMF was added into the solution of
(4-vinylphenyl)magnesium bromide (100 mmol) at 0 °C under N2,
stirred at room temperature overnight, and then quenched by
the addition of 50 mL of saturated NH4Cl solution. After extraction
with ethyl acetate, washing with brine, drying over MgSO4, filter-
ing, concentrating under vacuum, and purifying by flash column
chromatography on silica gel (volume ratio of petroleum ether to
EtOAc at 10), the 4-vinylbenzaldehyde (1, Fig. S1) as yellowish
oil (12.1 g, 91.7% yield) was finally obtained. 1H NMR (CDCl3,
400 MHz): d 9.98 (s, 1H, ArCHO), 7.83 (d, 2H, J = 8.0 Hz, ArH),
7.54 (d, 2H, J = 8.0 Hz, ArH), 6.76 (m, 1H, CH@), 5.90 (m, 1H,
@CH2), and 5.42 (m, 1H, @CH2) ppm. 13C NMR (CDCl3,
100.5 MHz): d 192.15 (ArCHO), 143.83 (ArC), 136.26 (C@), 136.03
(ArC), 130.49 (ArC), 127.13 (ArC), and 117.8 (@C) ppm.
formed on a Thermo ESCALAB 250 with Al Ka irradiation at h = 90°
for X-ray sources, and the binding energies were calibrated using
the C1s peak at 284.9 eV. UV–Vis spectra were recorded using a
Shimadzu UV2450 spectrometer. Thermal gravimetric analysis
(TGA) experiments were performed on a SDT Q600 V8.2 Build100
thermogravimetric analyzer under N2 flow. Inductively Coupled
Plasma Optical Emission Spectrometer (ICP-OES) experiments
were measured with a Perkin–Elmer plasma 40 emission spec-
trometer. The scanning electron microscopy (SEM) images of the
samples were recorded on a Hitachi SU 1510 apparatus. Transmis-
sion electron microscopy (TEM) experiments were performed on a
JEM-2100F field emission electron microscope (JEOL, Japan) with
an acceleration voltage of 110 kV. 1H NMR spectra were recorded
on a Bruker Avance-400 (400 MHz) spectrometer. Chemical shifts
were expressed in ppm downfield from TMS at d = 0 ppm. 13C
2.2.2. Synthesis of tetrastyrylporphyrin (TSP) monomer
The TSP was synthesized in a typical ‘‘one-pot” reaction accord-
ing to the literature [51]. Pyrrole (0.7 mL, 10 mmol) and
4-vinylbenzaldehyde (1.32 g, 10 mmol) were added to a flask

204
Z. Dai et al. / Journal of Catalysis 338 (2016) 202–209
(100.5 MHz) magic-angle spinning (MAS) NMR spectra were
recorded on a Varian infinity plus 400 spectrometer equipped with
a magic-angle spin probe in a 4-mm ZrO2 rotor.
4-bromovinylbenzene.
The
use
of
the
low-cost
4-bromovinylbenzene offers a good opportunity to widely apply
the POP-TPP. Particularly, the solvothermal polymerization pro-
vides a highly efficient strategy for construction of porphyrin mono-
mers into porous polymer as reflected by the quantitative yield of
the POP-TPP. In contrast, the syntheses of POPs from conventional
coupling reactions have relatively low yields [54]. After introduction
of various inorganic cations, a series of metalated POP-TPPs
(Co/POP-TPP, Zn/POP-TPP, and Mg/POP-TPP) were finally obtained.
Fig. 1 shows 13C MAS NMR spectrum of the POP-TPP, giving a
series of peaks ranged from 25 ppm to 150 ppm. Compare to TSP
monomer (Fig. S2), the POP-TPP appears additional peaks at
27.5 ppm and 41.0 ppm, which are assigned to those of polymer-
ized vinyl groups. At the same time, it almost cannot observe the
peak at 110.9 ppm related to the vinyl groups, indicating that the
POP-TPP has very high degree for the polymerization of the vinyl
groups. The peaks at 119–140 ppm in the POP-TPP are related to
the tetraphenylporphyrin group, which are well consistent with
those of the TSP monomer (Fig. S2). In contrast, the 1H MAS NMR
spectrum of POP-TPP (Fig. S3) is relatively poor, but we still can
distinguish the free pyrrole hydrogen in the porphyrin ring at
À2.13 ppm. This result is in good agreement with that of the
monomer in the liquid NMR (À2.75 ppm, Fig. S2), indicating that
the porphyrin structure in the sample is well retained after the
polymerization.
2.4. Catalytic cycloaddition of epoxides with CO2
Typically, the reactions were conducted in a Schlenk tube with
12.5 mmol of epoxides with CO2 purged at a balloon at room tem-
perature over the catalysts in the presence of tetrabutylammonium
bromide (n-Bu4NBr, 0.29 g, 0.9 mmol) for 24 h. The reactants and
products were determined by gas chromatography (Shimadzu
GC-2014C, a flame ionization detector) with a flexible quartz cap-
illary column coated with OV-17, where ethylbenzene was used as
an internal standard. The typical conditions were as follows: injec-
tion temperature at 220 °C; detection temperature at 240 °C;
column temperature at 60 °C for 2 min in the beginning, a ramp
of 10 °C/min to 220 °C and holding at 220 °C for 25 min. For the
conversion of styrene oxide, it was also analyzed by 1H NMR spec-
troscopy (Bruker Avance-400 spectrometer, 400 MHz) in the reac-
tion mixture. For catalytic evaluation under low CO2 concentration,
15% CO2 mixed with 85% N2 in volume was used and other condi-
tions were the same. For recycling tests, the catalyst was separated
by centrifugation, washed with EtOAc and CH2Cl2 for three times,
and dried under vacuum. Then, the catalyst was used for the next
run with addition of fresh n-Bu4NBr and epichlorohydrin.
Fig. 2A shows nitrogen sorption isotherms of the POP-TPP and
Co/POP-TPP. Both give typical curves of type I with type IV. The
steep increase below 0.1 of relative pressure (P/P0) is due to the
filling of the micropores, while the hysteresis loop higher than
0.40 (P/P0) is resulted from the contribution of mesoporosity and
macroporosity. Correspondingly, their pore sizes are mainly dis-
tributed at 0.4–2 nm and 12–150 nm (Fig. S4). The BET surface
areas of the POP-TPP and Co/POP-TPP are 1200 and 924 m2/g, with
a pore volume of 1.3 and 1.0 cm3/g, respectively. Similarly, the Mg/
POP-TPP and Zn/POP-TPP also exhibit high surface areas and large
3. Results and discussions
3.1. Catalyst characterization
Scheme 1 shows the synthesis of the porous porphyrin polymer,
POP-TPP, which was rationally prepared from solvothermal
polymerization of TSP monomer at 200 °C. The TSP monomer was
facilely
obtained
from
the
commercially
available
Scheme 1. Synthesis of POP-TPP and M/POP-TPP.

Z. Dai et al. / Journal of Catalysis 338 (2016) 202–209
205
stability of the POP-TPP structure in N2 flow before and after intro-
duction of Co species. Possibly, the interaction between the Co with
porphyrin rings could improve the thermal stability of Co/POP-TPP,
resulting in relatively low amount for the sample decomposition in
the final product.
f
e
N
H
N
N
d
d
H
N
Fig. 3 shows XPS spectra of the POP-TPP, Co/POP-TPP, and Co/
TPP. The N1s spectra of the POP-TPP exhibit two peaks at 399.8
and 397.7 eV, which is related to the contribution of two different
nitrogen pairs, that is, aminic nitrogen (ANHA) and iminic nitro-
gen (AN@) in the porphyrin ring. Interestingly, after the introduc-
tion of cobalt species and oxidation in the air, the Co/POP-TPP
exhibits N1s peak at 398.6 eV. After deconvolution, the sample
gives major N1s peaks at 399.8 and 398.6 eV. The peak at
398.6 eV is related to the coordination of cobalt species with por-
phyrin rings, while the peak at 399.8 eV is assigned to the shortage
of the metalation in the porphyrin rings [56]. The integrations of
the different parts of the XPS N1s signals show that the Co loading
is about 3.7 wt%, which is close to the value (3.2 wt%) obtained
from the ICP analysis. In contrast, if the porphyrin ring is fully met-
alated, the theoretical value should be 7.6 wt% (there is one Co site
in each porphyrin ring). This result also supports that the metala-
tion in the Co/POP-TPP is partial.
e
c
c
d
e
c
b
a
a
b
*
*
300
250
200
150
100
50
0
-50
-100
Chemical Shift (ppm)
Fig. 1. 13C MAS NMR spectrum of the POP-TPP. ‘‘⁄” The rotation bands.
pore volume (Fig. S5). Fig. 2B and C shows SEM and TEM images of
the POP-TPP respectively, giving direct evidence for the presence of
porosity in the POP-TPP. This porosity structure is very favorable
for the mass transfer in the reactions [55].
Fig. 2D shows thermogravimetric analysis (TGA) of the POP-TPP
and Co/POP-TPP in N2 flow, giving the polymer decomposition
temperature as high as 350 °C. This result suggests that the POP-
TPP has excellent thermal stability, which is very important for
catalytic applications in the organic transformations. Notably, the
Co/POP-TPP has less weight loss than the POP-TPP, which is not
consistent with the loading of Co (3.2 wt%) in the Co/POP-TPP. This
phenomenon might be related to the difference in the thermal
In addition, the sample Co2p spectra in the Co/POP-TPP show
the values of Co2p1/2 and Co2p3/2 at 796.1 and 780.5 eV respec-
tively, which is well consistent with those in the Co/TPP, giving
the values at 796.3 and 780.7 eV, respectively [57]. These values
are quite different from those (803.5, 797.9 eV and 787.2,
781.6 eV) in the starting salt of CoCl2Á6H2O. The disappearance of
the intense satellite lines (803.5 and 787.2 eV, due to the presence
of high spin Co2+ species) suggests that the cobalt species in the
Co/POP-TPP is in the +3 oxidation state [12,57].
UV–Vis spectroscopy is also used to exploit the Soret band of
the porphyrin polymer before and after the metalation. As shown
in Fig. S6, the POP-TPP has absorption peaks at 426, 515, 553,
1200
A
B
1000
800
b
600
400
200
0
a
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (P/P0)
100
90
80
70
60
50
C
D
b
a
0
100 200 300 400 500 600 700
T ( C)
°
Fig. 2. (A) N2 sorption isotherms, (B) SEM image, (C) TEM image, and (D) TG curves of (a) the POP-TPP and (b) Co/POP-TPP. Line b in (A) has been offset by 300 cm3/g along
with the vertical axis for clarity.

206
Z. Dai et al. / Journal of Catalysis 338 (2016) 202–209
A
B
398.6
780.5
796.1
d
780.7
781.6
d
a
796.3
399.8
c
397.7
803.5
797.9
787.2
b
410 408 406 404 402 400 398 396 394
Banding energy (eV)
810 805 800 795 790 785 780 775
Binding Energy (eV)
Fig. 3. (A) N1s and (B) Co2p XPS spectra of (a) POP-TPP, (b) CoCl2Á6H2O, (c) Co/TPP, and (d) Co/POP-TPP.
596, and 654 nm, which is consistent with those reported in
tetraphenylporphyrin (TPP) monomer (415, 515, 550, 590, and
650 nm) [51]. After introduction of transition metal cations, the
samples give new absorption peaks (Co/POP-TPP: 428, 526, 550,
597, and 657 nm; Zn/POP-TPP: 433, 524, 559, 602, and 658 nm;
Mg/POP-TPP: 430, 521, 562, 600, and 655 nm). In these spectra,
it is very difficult to observe the Soret bands, but it is very clear
to find the Q bands. The partial metalation could be supported
by the shift of the Q bands before and after the metalation. The
ICP measurements of Zn/POP-TPP and Mg/POP-TPP show that the
Zn and Mg loading is 4.5 wt% and 2.8 wt%, respectively.
It is worth noting that the Co/POP-TPP has superior chemical
stability. After treatment in the water solution for several days,
we cannot observe any cobalt species leaching. Even if the treat-
ment was conducted in strong acidic media (3 M HCl), only about
10% cobalt species are removed and the porous structure in the
polymer is still basically maintained (755 m2/g and pore volume
at 0.67 cm3/g, Fig. S7).
Fig. 4 shows CO2 sorption isotherms of POP-TPP, Co/POP-TPP,
and Co/TPP. Clearly, the porous organic polymer POP-TPP has a
good adsorption capacity with a value of 29.7 cm3/g at 25 °C under
1 atm CO2. After the metalation of cobalt, the Co/POP-TPP exhibits
a little high adsorption capacity (32.6 cm3/g at 25 °C under 1 atm
CO2). These results are comparable with those reported previously
[44,46,58]. In contrast, the Co/TPP has much lower adsorption
capacity. In addition, the Zn and Mg ions metalated porous organic
polymers (Zn/POP-TPP and Mg/POP-TPP) also show excellent CO2
adsorption capacity (34.6 and 37.5 cm3/g, Fig. S8) at 25 °C under
1 atm CO2. The enrichment of the CO2 in the nanopores is expected
to be beneficial for the promotion of the CO2 conversion [44,46].
3.2. Catalytic evaluation
Cycloaddition of epoxides with CO2 was chosen as a model for
the conversion of CO2. This reaction was investigated under pure
CO2 and a mixture of CO2 and N2 (15% CO2 + 85% N2 in volume).
3.2.1. Evaluation under pure CO2
Table 1 presents catalytic data in the cycloaddition of epichloro-
hydrin with CO2 to cyclic carbonate under ambient conditions
(29 °C and 1 atm) over various catalysts. Notably, the POP-TPP
gives the conversion at 52.1% (entry 1 in Table 1), but the Co/
POP-TPP exhibits the conversion at 95.6% (entry 2 in Table 1),
which is completely comparable with that of the homogeneous
Co/TPP catalyst (97.4%, entry 3 in Table 1). These results indicate
that the Co/POP-TPP is very active and cobalt species play an
important role for this reaction [12,59,60]. As control tests,
the reactions are performed with Co/POP-TPP and Co/TPP in the
absence of n-Bu4NBr or without Co/POP-TPP and Co/TPP in the
presence of n-Bu4NBr, as presented in Table 1 (entry 4–6). These
results also show the importance of the n-Bu4NBr in the cycloaddi-
tion reaction of epichlorohydrin with CO2.
When molar ratio of epoxide to catalyst (S/C, based on cobalt
species) is increased from 455 to 1820, the high conversion
(96.1%) can still be obtained with a long reaction time (96 h, entry
7 in Table 1). When the n-Bu4NBr amount is reduced from 290 mg
to 50 mg, the conversion has some decreases from 95.6% (entry 2 in
Table 1) to 88.9% (entry 8 in Table 1), confirming the importance of
n-Bu4NBr in the promotion of cycloaddition of CO2 and epoxides.
Fig. S10 shows the kinetic curves in the cycloaddition over the
Co/POP-TPP and Co/TPP catalysts. Under the same conditions, the
heterogeneous catalyst of Co/POP-TPP exhibits a little lower activ-
ity than the homogeneous catalyst of Co/TPP. Similarly, the activi-
ties of Zn/POP-TPP and Mg/POP-TPP (93.2% and 80.5%, entry 9 and
11 in Table 1) are also explored and show a little lower than those
of the Zn/TPP and Mg/TPP (93.5% and 99.3%, entry 10 and 12 in
Table 1). In addition, the TOFs of these metalated heterogeneous
catalysts have been calculated, and it is found that the TOF of
Co/POP-TPP (436 hÀ1) catalyst is higher than the TOF of the Zn/
POP-TPP (326 hÀ1) and Mg/POP-TPP (171 hÀ1) catalysts.
c
30
b
20
Fig. 5 shows the dependence of the activities on recycling num-
ber in the cycloaddition of epichlorohydrin with CO2 over the bin-
ary system of Co/POP-TPP and n-Bu4NBr. In each recycling, the
fresh epichlorohydrin and n-Bu4NBr were added. It is mentionable
that, after recycling for 18 times, the heterogeneous catalyst Co/
POP-TPP basically remains its activity, giving the conversion at
about 93.6% (Table 1, entry 13). Particularly, the cobalt species is
undetectable in the filtrate, which is reasonably attributed to the
superior chemical stability of the Co/POP-TPP. The BET surface area
of the Co/POP-TPP catalyst after recycling for 18 times is 507 m2/g
10
a
0
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (P/P0)
Fig. 4. CO2 sorption isotherms of (a) the Co/TPP, (b) POP-TPP and (c) Co/POP-TPP
measured at 25 °C.

Z. Dai et al. / Journal of Catalysis 338 (2016) 202–209
207
Table 1
Cycloaddition of epichlorohydrin with CO2 to form cyclic carbonate (Fig. S9) over various catalysts.
O
O
O
Ambient conditions
Solvent-free
O
Cl
CO2
+
Cl
Entry
Catalysts
Additives
Temp. (°C)
Time (h)
Conv. (%)a
Select. (%)a
1b
2c
POP-TPP
Co/POP-TPP
Co/TPP
Co/POP-TPP
Co/TPP
None
Co/POP-TPP
Co/POP-TPP
Zn/POP-TPP
Zn/TPP
Mg/POP-TPP
Mg/TPP
n-Bu4NBr
n-Bu4NBr
n-Bu4NBr
None
29
29
29
29
29
29
29
29
29
29
29
29
29
24
24
24
24
24
24
96
24
24
24
24
24
24
52.1
95.6
97.5
9.7
18.5
34.0
96.1
88.9
93.2
93.5
80.5
99.3
93.6
>99.0
99.0
99.0
99.0
99.0
99.0
99.0
99.0
>99.0
>99.0
>99.0
>99.0
99.0
3c
4
5
6
None
n-Bu4NBr
n-Bu4NBr
n-Bu4NBr
n-Bu4NBr
n-Bu4NBr
n-Bu4NBr
n-Bu4NBr
n-Bu4NBr
7d
8e
9f
10f
11g
12g
13h
Co/POP-TPP
a
b
c
Determined by GC analysis.
48 mg of POP-TPP was used.
50 mg of Co/POP-TPP (1.6 mg Co) or 19 mg of Co/TPP (1.6 mg Co) was used.
Co/POP-TPP catalyst (12.5 mg, 0.4 mg Co).
d
e
f
50 mg of n-Bu4NBr.
50 mg of Zn/POP-TPP (2.3 mg Zn) or 23.5 mg of Zn/TPP (2.3 mg Zn) was used.
50 mg of Mg/POP-TPP (1.4 mg Mg) or 37.0 mg of Mg/TPP (1.4 mg Mg) was used.
Recycles for 18 times.
g
h
with pore volume of 0.60 cm3/g (Fig. S11). The reduction of the
surface area and pore volume might be due to accumulation of
the by-products in the pores of the heterogeneous catalyst. These
results indicate that the heterogeneous catalyst Co/POP-TPP has
excellent recyclability for the cycloaddition, which should be
potentially important for industrial applications of this heteroge-
neous catalyst.
Table 2 presents catalytic data in the cycloaddition of propylene
oxide (entry 1 in Table 2, Fig. S12), 1,2-epoxyhexane (entry 2 in
Table 2, Fig. S13), allyl glycidyl ether (entry 3 in Table 2,
Fig. S14), styrene oxide (entry 4 in Table 2, Fig. S15), and butyl
glycidyl ether (entry 5 in Table 2, Fig. S16) with CO2 over the
Co/POP-TPP catalyst. This catalyst is still active for the conversion
of these epoxides, but the activities are strongly dependent on their
structures. Clearly, size-dependent catalysis is observed when
using the substrates with larger dimensions which give rise to
lower activities.
b
100
a
80
60
40
20
0
0
2
4
6
8
10 12 14 16 18 20
Recycles
Fig. 5. Conversion (a) and selectivity (b) of the recycling tests in the cycloaddition
of epichlorohydrin with CO2 over the Co/POP-TPP catalyst.
Table 2
Cycloaddition of CO2 with various substrates over the Co/POP-TPP catalyst.a
Entry
1
Epoxide
Product
T (°C)
Time (h)
24
Conv. (%)b
95.8
Select. (%)b
99.0
O
O
29
O
O
O
O
2
3
29
29
24
48
88.0
85.5
99.0
99.0
O
O
O
O
O
O
O
O
77.9c (74.2)c
68.6 (88.8)
99.0
99.0
O
O
4
5
29 (50)
29 (50)
118 (48)
72 (48)
O
O
O
O
O
O
O
O
a
b
c
Reaction conditions: substrate (12.5 mol), Co/POP-TPP catalyst (50 mg, 1.6 mg Co), n-Bu4NBr (0.29 g), and 1 atm CO2.
Determined by GC analysis.
Determined by liquid NMR.

208
Z. Dai et al. / Journal of Catalysis 338 (2016) 202–209
100
90
80
70
60
50
40
30
20
10
low CO2 concentration (15% CO2 + 85% N2 in volume, similar to
the emission of CO2 in industrial processes), the heterogeneous
catalyst of Co/POP-TPP shows even better activity than the homo-
geneous catalyst of Co/TPP. The high activity and recyclability of
the Co/POP-TPP in the cycloaddition reaction of epoxides and
CO2 to form cyclic carbonate under very mild reaction condition
might offer an opportunity to design an efficient heterogeneous
catalyst for chemical fixation of CO2 in the future.
d
c
b
Acknowledgments
a
15% CO
2
+ 85% N
2
This work was supported by the National Natural Science
Foundation of China (21333009, 21422306 and 91545111) and
Fundamental Research Funds for the Central Universities
(2015XZZX004-04) and Zhejiang Provincial Natural Science
Foundation of China under Grant No. LR15B030001.
10
20
30
40
50
60
70
80
Time (h)
Fig. 6. The dependences of (a and b) conversion and (c and d) selectivity in the
cycloaddition of epichlorohydrin (12.5 mmol) with CO2 on reaction time over (a and
c) the Co/TPP (1.6 mg Co) and (b and d) Co/POP-TPP catalysts (1.6 mg Co) under low
CO2 concentration (1 atm pressure, 15% CO2 mixed with 85% N2) at 29 °C with
co-catalyst of n-Bu4NBr (50 mg).
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.jcat.2016.03.005.
3.2.2. Evaluation under Low CO2 concentration
Because the emission of CO2 in industrial processes normally
has low concentration (below 15%), the investigation on the
cycloaddition under relatively low CO2 concentration should be
more significant than that under pure CO2.
References
[1] H. Arakawa, M. Aresta, J.N. Armor, M.A. Barteau, E.J. Beckman, A.T. Bell, J.E.
Bercaw, C. Creutz, E. Dinjus, D.A. Dixon, K. Domen, D.L. DuBois, J. Eckert, E.
Fujita, D.H. Gibson, W.A. Goddard, D.W. Goodman, J. Keller, G.J. Kubas, H.H.
Kung, J.E. Lyons, L.E. Manzer, T.J. Marks, K. Morokuma, K.M. Nicholas, R.
Periana, L. Que, J. Rostrup-Nielson, W.M.H. Sachtler, L.D. Schmidt, A. Sen, G.A.
Somorjai, P.C. Stair, B.R. Stults, W. Tumas, Chem. Rev. 101 (2001) 953.
[2] B. Schäffner, F. Schäffner, S.P. Verevkin, A. Börner, Chem. Rev. 110 (2010) 4554.
[3] O.V. Zalomaeva, A.M. Chibiryaev, K.A. Kovalenko, O.A. Kholdeeva, B.S.
Balzhinimaev, V.P. Fedin, J. Catal. 298 (2013) 179.
[4] A. Decortes, A.M. Castilla, A.W. Kleij, Angew. Chem. Int. Ed. 49 (2010) 9822.
[5] H.S. Kim, J.J. Kim, H. Kim, H.G. Jang, J. Catal. 220 (2003) 44.
[6] Z.-Z. Yang, L.-N. He, C.-X. Miao, S. Chanfreau, Adv. Synth. Catal. 352 (2010)
2233.
Fig. 6 shows dependence of the activities on the reaction time in
the cycloaddition of epichlorohydrin with CO2 over the Co/POP-TPP
and Co/TPP catalysts under low CO2 concentration (15% CO2 + 85%
N2 in volume, 1 atm) at 29 °C. Very interestingly, the activities over
the Co/POP-TPP are obviously higher than those over the Co/TPP.
For example, when the reaction time reaches to 48 h, the
Co/POP-TPP gives the conversion at 45.4% and the selectivity at
88.7%, while the Co/TPP exhibits the conversion at 37.4% and the
selectivity at 81.0%. Considering the same catalytically active sites
between the Co/POP-TPP and Co/TPP and higher activities over the
Co/TPP than those over the Co/POP-TPP in the cycloaddition under
pure CO2, we suggest that higher activities over the Co/POP-TPP
than those over the Co/TPP under low CO2 concentration (15% in
volume) are reasonably attributed to the contribution of the poros-
ity in the Co/POP-TPP. Possibly, the presence of sample porosity is
favorable for enrichment of CO2 to the nearby the active sites in the
Co/POP-TPP, effectively improving the reaction rate. Similar phe-
nomena have been reported previously [55,61–63]. In addition,
this suggestion is also strongly supported by the CO2 adsorption
on the Co/POP-TPP and Co/TPP, as evidenced in Fig. 4. For example,
under relative pressure of CO2 at 0.15, the porous Co/POP-TPP has
adsorption capacity of CO2 at 8 cm3/g (16 mg/g), while the non-
porous Co/TPP almost does not adsorb CO2. Obviously, higher
activities over the heterogeneous catalyst of Co/POP-TPP than
those over the homogeneous catalyst of Co/TPP under low CO2
concentration are potentially important for applications of CO2
emission in industrial processes.
[7] Y. Ren, J.-J. Shim, ChemCatChem 5 (2013) 1344.
[8] R.L. Paddock, S.T. Nguyen, J. Am. Chem. Soc. 123 (2001) 11498.
[9] X.-B. Lu, Y.-J. Zhang, K. Jin, L.-M. Luo, H. Wang, J. Catal. 227 (2004) 537.
[10] H. Jing, S.K. Edulji, J.M. Gibbs, C.L. Stern, H. Zhou, S.T. Nguyen, Inorg. Chem. 43
(2004) 4315.
[11] A. Decortes, M.M. Belmonte, J. Benet-Buchholz, A.W. Kleij, Chem. Commun. 46
(2010) 4580.
[12] X.-B. Lu, D.J. Darensbourg, Chem. Soc. Rev. 41 (2012) 1462.
[13] C. Martin, C.J. Whiteoak, E. Martin, M.M. Belmonte, E.C. Escudero-Adán, A.W.
Kleij, Catal. Sci. Technol. 4 (2014) 1615.
[14] W.J. Kruper, D.D. Dellar, J. Org. Chem. 60 (1995) 725.
[15] T. Ema, Y. Miyazaki, S. Koyama, Y. Yano, T. Sakai, Chem. Commun. 48 (2012)
4489.
[16] T. Ema, Y. Miyazaki, J. Shimonishi, C. Maeda, J.-Y. Hasegawa, J. Am. Chem. Soc.
136 (2014) 15270.
[17] Y. Qin, H. Guo, X. Sheng, X. Wang, F. Wang, Green Chem. 17 (2015) 2853.
[18] C. Maeda, T. Taniguchi, K. Ogawa, T. Ema, Angew. Chem. Int. Ed. 54 (2015) 134.
[19] T. Yano, H. Matsui, T. Koike, H. Ishiguro, H. Fujihara, M. Yoshihara, T.
Maeshima, Chem. Commun. (1997) 1129.
[20] K. Yamaguchi, K. Ebitani, T. Yoshida, H. Yoshida, K. Kaneda, J. Am. Chem. Soc.
121 (1999) 4526.
[21] H. Yasuda, L.-N. He, T. Sakakura, J. Catal. 209 (2002) 547.
[22] M. Tu, R.J. Davis, J. Catal. 199 (2001) 85.
[23] E.J. Doskocil, S.V. Bordawekar, B.G. Kaye, R.J. Davis, J. Phys. Chem. B 103 (1999)
6277.
[24] Y. Du, F. Cai, D.-L. Kong, L.-N. He, Green Chem. 7 (2005) 518.
[25] J. Sun, S.-I. Fujita, F. Zhao, M. Hasegawa, M. Arai, J. Catal. 230 (2005) 398.
[26] R. Srivastava, D. Srinivas, P. Ratnasamy, J. Catal. 233 (2005) 1.
[27] M. Ramin, J.-D. Grunwaldt, A. Baiker, J. Catal. 234 (2005) 256.
[28] Y. Xie, Z. Zhang, T. Jiang, J. He, B. Han, T. Wu, K. Ding, Angew. Chem. Int. Ed. 46
(2007) 7255.
[29] W.-L. Dai, B. Jin, S.-L. Luo, X.-B. Luo, X.-M. Tu, C.-T. Au, Catal. Today 233 (2014)
92.
[30] J. Song, Z. Zhang, S. Hu, T. Wu, T. Jiang, B. Han, Green Chem. 11 (2009) 1031.
[31] J. Kim, S.-N. Kim, H.-G. Jang, G. Seo, W.-S. Ahn, Appl. Catal. A: Gen. 453 (2013)
175.
[32] W. Clegg, R.W. Harrington, M. North, R. Pasquale, Chem. Eur. J. 16 (2010) 6828.
[33] M. North, B. Wang, C. Young, Energy Environ. Sci. 4 (2011) 4163.
[34] N. Takeda, S. Inoue, Bull. Chem. Soc. Jpn. 51 (1978) 3564.
[35] T. Aida, S. Inoue, J. Am. Chem. Soc. 105 (1983) 1304.
[36] J. Meléndez, M. North, R. Pasquale, Eur. J. Inorg. Chem. (2007) 3323.
4. Conclusion
In summary,
a porphyrin based porous organic polymer
(POP-TPP) is successfully synthesized from polymerization of
vinyl-functionalized porphyrin monomer. After metal coordina-
tion, the catalysts (Co/POP-TPP, Zn/POP-TPP, and Mg/POP-TPP)
with n-Bu4NBr as a nucleophilic additive are really active in
heterogeneous cycloaddition of epoxides with CO2 to cyclic
carbonates under ambient conditions. Particularly, the heteroge-
neous Co/POP-TPP catalyst can recycle for 18 times and the activity
was remained. When this reaction is performed under relatively

Z. Dai et al. / Journal of Catalysis 338 (2016) 202–209
209
[37] M. North, R. Pasquale, Angew. Chem. Int. Ed. 48 (2009) 2946.
[38] A.W. Kleij, Dalton Trans. (2009) 4635.
[39] P. Yan, H. Jing, Adv. Synth. Catal. 351 (2009) 1325.
[40] D. Bai, S. Duan, L. Hai, H. Jing, ChemCatChem 4 (2012) 1752.
[41] R. Luo, X. Zhou, S. Chen, Y. Li, L. Zhou, H. Ji, Green Chem. 16 (2014) 1496.
[42] J. Meléndez, M. North, P. Villuendas, C. Young, Dalton Trans. 40 (2011) 3885.
[43] T. Ema, Y. Miyazaki, T. Taniguchi, J. Takada, Green Chem. 15 (2013) 2485.
[44] Y. Xie, T.-T. Wang, X.-H. Liu, K. Zou, W.-Q. Deng, Nat. Commun. 4 (2013) 1960.
[45] W.-Y. Gao, Y. Chen, Y. Niu, K. Williams, L. Cash, P.J. Perez, L. Wojtas, J. Cai, Y.-S.
Chen, S. Ma, Angew. Chem. Int. Ed. 53 (2014) 2615.
[52] R.W. Wagner, T.E. Johnson, J.S. Lindsey, J. Am. Chem. Soc. 118 (1996) 11166.
[53] J.S. Lindsey, J.N. Woodford, Inorg. Chem. 34 (1995) 1063.
[54] L. Chen, Y. Yang, D. Jiang, J. Am. Chem. Soc. 132 (2010) 9138.
[55] F. Liu, L. Wang, Q. Sun, L. Zhu, X. Meng, F.-S. Xiao, J. Am. Chem. Soc. 134 (2012)
16948.
[56] Z. Xiang, Y. Xue, D. Cao, L. Huang, J.-F. Chen, L. Dai, Angew. Chem. Int. Ed. 53
(2014) 2433.
[57] D.C. Frost, C.A. McDowell, I.S. Woolsey, Mol. Phys. 27 (1974) 1473.
[58] X.-H. Liu, J.-G. Ma, Z. Niu, G.-M. Yang, P. Cheng, Angew. Chem. Int. Ed. 54
(2015) 988.
[46] Y. Xie, T.-T. Wang, R.-X. Yang, N.-Y. Huang, K. Zou, W.-Q. Deng, ChemSusChem
7 (2014) 2110.
[59] R.L. Paddock, Y. Hiyama, J.M. McKay, S.T. Nguyen, Tetrahedron Lett. 45 (2004)
2023.
[47] Y. Zhang, S.N. Riduan, Chem. Soc. Rev. 41 (2012) 2083.
[48] P. Kaur, J.T. Hupp, S.T. Nguyen, ACS Catal. 1 (2011) 819.
[49] Q. Sun, M. Jiang, Z. Shen, Y. Jin, S. Pan, L. Wang, X. Meng, W. Chen, Y. Ding, J. Li,
F.-S. Xiao, Chem. Commun. 50 (2014) 11844.
[50] A.M. Shultz, O.K. Farha, J.T. Hupp, S.T. Nguyen, Chem. Sci. 2 (2011) 686.
[51] C.E. Anderson, S.I. Vagin, W. Xia, H. Jin, B. Rieger, Macromolecules 45 (2012)
6840.
[60] X. Jiang, F. Gou, H. Jing, J. Catal. 313 (2014) 159.
[61] Q. Sun, Z. Dai, X. Liu, N. Sheng, F. Deng, X. Meng, F.-S. Xiao, J. Am. Chem. Soc.
137 (2015) 5204.
[62] Q. Sun, Z. Dai, X. Meng, L. Wang, F.-S. Xiao, ACS Catal. 5 (2015) 4556.
[63] Q. Sun, Z. Dai, X. Meng, F.-S. Xiao, Chem. Soc. Rev. 44 (2015) 6018.